Effects of niobium substitution on crystal structure and physical properties of mayenite Ca₁₂Al₁₄O₃₃

Abstract

Mayenite (Ca12Al14O33) is a functional oxide with potential in high-temperature and photonic applications, whose properties can be tuned via cation substitution. We report the successful substitution of niobium for aluminium in phase-pure mayenite (Ca12Al14-xNbxO33+x) using conventional solid-state synthesis (x ≤ 0.35). The successful incorporation of Nb was verified by Rietveld refinement, X-ray fluorescence, and energy-dispersive X-ray spectroscopy. Increasing Nb content leads to a linear increase in the melting point up to 1406 °C (x = 0.35), the emergence of pronounced photoluminescence in Nb-substituted mayenite, as well as distinct and systematic shifts in the Raman spectra, all depending on the substitution level. Notably, we reveal that both photoluminescence intensity and band gap energies are directly correlated with lattice strain, which is strongly influenced by the synthesis temperature. These findings provide new insight into the interplay between transition metal substitution, defects, and processing conditions, and demonstrate accessible routes to tailor the structure and optical properties of mayenite for photonic and high-temperature ceramic applications.